In the production of semiconductor devices such as IC cards, solar cells and thin film transistors or semiconductor integrated circuits, miniaturization of devices or degree of freedom concerning use thereof can be improved by making thickness of semiconductor wafers used as substrates therefor sufficiently thinner.
In particular, for IC cards and so forth, necessity for thinning semiconductor wafer is high, and it is desired that chips constituting circuits should be made thinner as much as possible.
In a conventional technique, in order to produce such a thin semiconductor wafer, semiconductor devices (circuit patterns) are formed on a surface of a mirror-polished semiconductor wafer having such a usual thickness as described later, then a protective tape is adhered on the surface, the wafer is placed on a chuck table of grinding apparatus with the surface side as the underside, and the back surface is ground with a grinding stone to thin the wafer (see, for example, Japanese Patent Laid-open (Kokai) Publication No. 5-218196 and 8-37169).
The aforementioned usual thickness of semiconductor wafer generally varies depending on its diameter and, for example, it is about 625 μm for a wafer having a diameter of 5 inches (125 mm) or 6 inches (150 mm) or about 725 μm for a wafer having a diameter of 8 inches (200 mm). And although the thickness after thinning may vary depending on types of semiconductor devices to be produced, it is generally about 150-400 μm. If it is attempted to thin wafers further thinner by using the aforementioned conventional technique, the probability of breakage of the wafer during the processing step or upon peeling of the protective tape becomes high, and therefore it is extremely difficult to use it for large scale production.
However, semiconductor devices used for IC cards and so forth are required to have increasingly various functions in recent years. Under such a situation, necessity of thinning semiconductor wafers to be used further thinner has become higher, and it has become necessary to make them thinner to a thickness of about 120 μm or smaller.
If the conventional method for thinning wafers is used in order to produce such an extremely thin semiconductor wafers, frequency of breakage such as cracking or chipping during the processing step and so forth becomes higher as described above. Therefore, yield is degraded and cost is increased. As a result, it cannot meet large scale production. That is, if it is attempted to obtain a thickness of 120 μm or less by the conventional technique, it is substantially impossible to prevent cracking unless a wafer having a diameter of 4 inches (100 mm) or less is used.